Triode electron tube with segmented cathode and vane grid

ABSTRACT

A high power, high frequency triode electron tube having a cylindrical segmented cathode with a coaxial cylindrical vane or bar type grid.

. United States Patent 1191 [111 3,814,972 Sain June 4, 1974 [54] TRIODE ELECTRON TUBE WITH 2,358,542 9/!944 Thompson .i 313/299 SEGMENTED CATHODE AND VANE GRID 2.459.84l l/l949 Rouse 3l3/356 2,544,664 3/l95l Garner et al 3l3/l9 5] inventor: William H- Sain, San Mate0,Cal1f- 2,883,576 4/1959 Harries 313/246 [73] Assignee: Varian Associates, Palo Alto, Calif. 22 Filed: May 3 1973 Primary Examiner.lames w. Lawrence Assistant Examiner-William H. Punter [21] Appl' 356,855 Attorney, Agent, or Firm-Stanley Z. Cole; John J'.

Related US. Application Data Morrissey [63] Continuation of Ser. No. l6l,456, July- 12, [97],

abandoned.

[52] U.S. Cl 313/296, 313/302, 313/338 [57] ABSTRACT [51] Int. Cl H0lj 1/46, HOlj 19/38 Field of Search 296', A high power, high frequency triode electron tube 8, 2 5 having a cylindrical segmented cathode with a coaxial cylindrical vane or bar type grid. [56] References Cited 1 UNITED STATES PATENTS 14 Claims, 4 Drawing Figures 2,204,306 6/1940 Harris 3l3/3 l iL --|moui1e ll l' 'i WITH e f] 11". l 6 i l i ll 1'' I 4 ii 1 8 il 46 n ll :11. c I 2" I l m 44 F PATENTEDJM 4mm 3314372 SHEEI 1 0f 2 I NVEN'TOR l6 WILLIAM H. SAIN MQYiLQL ATTORNEY PATENTEDJUH 41974 SHEEI 2 (If 2 WITHOUT e VFIG.2

INVENTOR. WILLIAM H. SAIN ATTORNEY TRIODE ELECTRON TUBE WITH SEGMENTED CATHODE AND VANE GRID This is a continuation division of application .Ser. No. 161,456 filed July 12, I971, now abandoned.

BACKGROUND OF THE INVENTION OBJECTS AND SUMMARY OF THE INVENTION It is, therefore, a general object of the invention to provide an improved triode electron tube.

It is another object of the invention to provide a high power triode tube which has relatively low grid current.

In accordance with the above objects there is'provided a triode electron tube having electrode structures comprising a hollow anode. A cylindrical cathode is coaxial within the anode and has on its outer surface a plurality of alternately located electron emitting and non-emitting areas. A cylindrical control grid is coaxial with the cathode and comprised of equally spaced barlike members of elongated cross section. The long axis of the cross section is radially aligned with the nonemitting areas.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a cross-sectional view of a triode electron tube embodying the invention;

FIG. 2 is an enlarged fragmentary sectional view taken along the line 2-2 of FIG. I;

FIG. 2A is an enlarged fragmentary sectional view of an alternative embodiment of the cathode structure of the invention; and 1 FIG. 3 is a circuit diagram showing a typical use of the triode'tube of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. I shows in cross-sectional format the electrode structures of the present invention. These include an anode assembly 10, a grid assembly 11 and a cathode assembly 12. All are mounted on a base assembly 13 which includes a ceramic base disc 14 through which the various connection pins I6 extend. Anode assembly 10 includes a hollow metal cylindrical anode 17 which has mounted on it a cooler jacket 18 with cooling fins 19. The tip 21 of anode I7 is sealed after a vacuum is drawn on the tube and a protective cap 22 placed over it. Anode 17 is brazed to an anode deck 23 which is connected to anode flange 24 through a ceramic ring 26. Anode flange 24 in turn is connected to ceramic base 14 by the base mounting flange 27. This flange also supports, through a cone 25, grid bars 28 (detailed in FIG. 2) which are mounted coaxially with anode 17 along the axis 29. A grid cap 30 is affixed to the top of the cylindrical cage formed by gridbars 28.

Cathode assembly 12 encloses a wound heater element 31 supported by heater leads 32 and 33 which are coupled to appropriate pins 16. A cathode cup 34 (detailed in FIG. 2) is mounted over the heater element 31 and supported by the structure 36. The cylindrical cathode is maintained coaxial along the axis 29 with the grid cup 28 and the anode 17 by an alignment pin 35 extending from grid cap 30.

A typical cross section of the cathode-grid-anode structure is illustrated in FIG. 2. The cathode is of the segmented type and is in the form of a metal cylinder with shallow longitudinal grooves 41 being cut into the outer surface and equally spaced around the periphery.

Lands 42 lie between the grooves. A thermonionic electron emitting substance such as barium-strontium mixture either partially or completely fills the grooves, as described more fully below, and provides an electron emitting area 43.

Various critical dimensions are shown including dimension A, the distance from the top of land 42 to the surface of the emitting area 43; dimension B, the width of bars 46; dimension C, the depth of grid bar 46; dimension D, the distance between the edges of adjacent lands 42; dimension E, the distance between the center line of lands 42; dimension F, the distance between the bars 46 and the emitting area 43; and dimension G,- the distance between anode l7 and the end of grid bar 46.

Grid 28 is composed of a cylindrical array of equally spaced bar-like members 46 which are substantially V elongated in cross section. Members 46 may be constructed by squashing circular wires until they have a substantially rectangular cross section. Another configuration which has been successfully used is two normal round grid-wires placed contiguously to form an elongated cross section. The long axis of the cross section is radially aligned with the non-emitting areas or lands In the usual triode, amplification is normally increased by increasing the density of grid wires but at a sacrifice of greater grid current. In the present invention, rather than increase the density of the grid bars, the depth or dimension C is increased to provide higher amplification. The segmented cathode directs the flow of electrons to restrict the amount of grid current.

Increasing dimension C relative to dimensions D and B increases the amplification factor of the tube because of the increased electrostatic shielding created between the anode and the cathode. However, such an increase alone results in increased grid current because the elongated grid bars will intercept the electron beam. This problem is overcome, as clearly illustrated in FIG. 2, by recessing the emitting area 43 relative to the land 42 and by making the transition between the two a sharp step 44. This recession provides better focusing of the electron beam because the step acts as a lens to deflect electrons inwardly towards the center of the beam. For tubes of typical sizes, such as the tubes described below, the desired focusing effect is achieved when the dimension A does not exceed 0.004 inch. For short bars, where interception of the electron beam to form grid current is less of a problem, the step may be eliminated by making the dimension A zero as shown in FIG. 2A where the outer surface of the emitting area 43 is flush with the outer surface of the land 42. Here, however, the separation of land 42 from emitting areas 43 should still be sharp because some lens effect is still required in order to give a well defined beam. Otherwise electrons at the edges of the beam will be intercepted by the grid resulting in grid current. Additional focusing, especially where dimension A is small, occurs when the width of the bars 46, dimension 8, is slightly less than the width of the land area 42.

One of the desirable characteristics of the triode of the present invention is the low amount of current, 1).. intercepted by the control grid 28 as compared to the plate current, i,,, at relatively high positive grid voltages. This is achieved by the provision of a highly convergent beam such as shown at 47. This beam characteristic is obtained by the unique construction of the cathode 34 and grid 28. Beam 47 is shown as the tube would be in operation with an input control signal designated e The following Table 1 shows the dimensions A through G in three different sizes of the tubes which were built and operated and which achieved ratios of plate to grid current (i /i.) of from five to ten percent with amplification factors varying from 300 to 1,200.

TABLE 1.D]MENSIONS lN INCHES periment Ampli- Numfication her A B C D E F G factor The foregoing tubes had a common cathode diameter of approximately .344 inches with a control grid of 56 TABLE 2.DlMENSlONS lN- INCHES W Amplification A B C D E F G factor It will be seen from Tables 1 and 2 that the ratio of the distance between adjacent nonemitting areas to the distance between symmetrically positioned centerlines on adjacent non-emitting areas, i.e., the ratio D/E, is within the range from 0.575 to 0.735. It can also be seen from Tables 1 and 2 that the ratio of the distance between any nonemitting area and the bar-like grid member adjacent thereto to the distance between any two adjacent nonemitting areas. i.e., the ratio (F-A)/D, is within the range from 0.400 to 0.478.

The unique grid cathode electrode configuration of the triode of the present invention also provides a relatively low idling, or no load, cathode-to-anode current which is shown in FIG. 2 as the relatively narrow electron beam 48. This is without the e signal being supplied. Such low current is important in providing greater efficiency since this idling current is a total heat loss when the circuit has no applied signal.

FIG. 3 illustrates a typical circuit environment of the triode tube of the present invention where it is shown as operating as a cathode driven amplifier. The drive voltage a is supplied through the tuned transformer 51. A power supply 5,2 provides a dc voltage E through an inductance 53. The output voltage e ls'supplied to a tuned circuit 54 through a capacitor 56 and the tuned circuit is coupled to an antenna 57. Because of the high amplification factor no bias is required in the cathode circuit.

With the unique cathode-grid design of the present invention a high amplification factor triode tube is provided which requires relatively simple circuitry as shown in F IG. 3. The present tube will achieve grid currents of less than ten percent of the plate current while v in a conventional high amplification factor triode the grid current may be 30 to 40 percent of the plate current for the same grid and plate voltages.

I claim:

1. An electron tube comprising:

a cylindrical anode;

a cylindrical cathode disposed coaxially within said anode, the surface of said cathode which faces said anode comprising a plurality of alternately located electron emitting and nonemitting areas, the boundaries between adjacent emitting and nonemitting areas being parallel to the axis of said cylindrical cathode, the ratio of the distance between said adjacent nonemitting areas to the distance between symmetrically positioned centerlines on adjacent nonemitting areas parallel to said cylinder axis being substantially within the range from 0.575 to 0.735, a heater being disposed inside said cathode; and

electron control means consisting of only one control grid, said control grid being cylindrical and disposed within said anode coaxially with respect to said anode and cathode, said control grid consisting of bar-like members of elongate cross section, the long axis of said cross section of each one of said bar-like grid members being radially aligned with a distinct one of said nonemitting areas of said cathode whereby for adjacent bar-like grid members the ends of said long axes distal said cathode are further apart from each other than the ends of said bar-like grid members proximal to said cathode are from each other.

2. The electron tube of claim 1 wherein said nonemitting areas have a width slightly greater than the width of the short axis of the cross section of each of said barlike control grid members.

3. The electron tube of claim 1 wherein the transition between said emitting and nonemitting areas is a sharp step.

4. The electron tube of claim 3 wherein said emitting areas are recessed below the surface of said nonemitting areas.

5. The electron tube of claim 1 wherein said cross section is substantially rectangular.

' 6. The electron tube of claim 1 wherein said emitting areas are flush with said nonemitting areas.

7. The electron tube of claim 1 wherein said nonemitting areas extend radially outward beyond said emitting areas by an amount not exceeding 0.004 inch.

8. An electron tube comprising:

a cylindrical anode;

a cylindrical cathode disposed coaxially within said anode, the surface of said-cathode which faces said anode comprising a plurality of alternately located electron emitting and nonemitting areas, a heater being disposed inside said cathode; and

electron control means consisting of only one control grid, said control grid being cylindrical and disposed within said anode coaxially with respect to said anode and cathode, said control grid consisting of bar-like members of elongate cross section, the long axis of said cross section of each one of said bar-like grid members being radially aligned with a distinct one of said nonemitting areas of said cathode whereby for adjacent bar'like grid members the ends of said long axes distal said cathode are further apart from each other than the ends of said bar-like grid members proximal to said cathode are from each other, the ratio of the distance between each nonemitting area and the bar-like grid member adjacent thereto to the distance between any two adjacent nonemitting areas being substantially in the range from 0.400 to 0.478.

9. The electron tube of claim 8 wherein said nonemitting areas have a width slightly greater than the width of the short axis of the cross section of each of said barlike control grid members.

10. The electron tube of claim 8 wherein the transition between said emitting and nonemitting areas is a sharp step.

11. The electron tube of claim 10 wherein said emitting areas are recessed below the surface of said nonemitting areas.

12. The electron tube of claim 8 wherein said cross section is substantially rectangular.

13. The electron tube of claim 8 wherein said emitting areas are flush with said nonemitting areas.

14. The electron tube of claim 8 wherein said nonemitting areas extend radially outward beyond said emitting areas by an amount not exceeding 0.004 inch. 

1. An electron tube comprising: a cylindrical anode; a cylindrical cathode disposed coaxially within said anode, the surface of said cathode which faces said anode comprising a plurality of alternately located electron emitting and nonemitting areas, the boundaries between adjacent emitting and nonemitting areas being parallel to the axis of said cylindrical cathode, the ratio of the distance between said adjacent nonemitting areas to the distance between symmetrically positioned centerlines on adjacent nonemitting areas parallel to said cylinder axis being substantially within the range from 0.575 to 0.735, a heater being disposed inside said cathode; and electron control means consisting of only one control grid, said control grid being cylindrical and disposed within said anode coaxially with respect to said anode and cathode, said control grid consisting of bar-like members of elongate cross section, the long axis of said cross section of each one of said barlike grid members being radially aligned with a distinct one of said nonemitting areas of said cathode whereby for adjacent bar-like grid members the ends of said long axes distal said caThode are further apart from each other than the ends of said bar-like grid members proximal to said cathode are from each other.
 2. The electron tube of claim 1 wherein said nonemitting areas have a width slightly greater than the width of the short axis of the cross section of each of said bar-like control grid members.
 3. The electron tube of claim 1 wherein the transition between said emitting and nonemitting areas is a sharp step.
 4. The electron tube of claim 3 wherein said emitting areas are recessed below the surface of said nonemitting areas.
 5. The electron tube of claim 1 wherein said cross section is substantially rectangular.
 6. The electron tube of claim 1 wherein said emitting areas are flush with said nonemitting areas.
 7. The electron tube of claim 1 wherein said nonemitting areas extend radially outward beyond said emitting areas by an amount not exceeding 0.004 inch.
 8. An electron tube comprising: a cylindrical anode; a cylindrical cathode disposed coaxially within said anode, the surface of said cathode which faces said anode comprising a plurality of alternately located electron emitting and nonemitting areas, a heater being disposed inside said cathode; and electron control means consisting of only one control grid, said control grid being cylindrical and disposed within said anode coaxially with respect to said anode and cathode, said control grid consisting of bar-like members of elongate cross section, the long axis of said cross section of each one of said bar-like grid members being radially aligned with a distinct one of said nonemitting areas of said cathode whereby for adjacent bar-like grid members the ends of said long axes distal said cathode are further apart from each other than the ends of said bar-like grid members proximal to said cathode are from each other, the ratio of the distance between each nonemitting area and the bar-like grid member adjacent thereto to the distance between any two adjacent nonemitting areas being substantially in the range from 0.400 to 0.478.
 9. The electron tube of claim 8 wherein said nonemitting areas have a width slightly greater than the width of the short axis of the cross section of each of said bar-like control grid members.
 10. The electron tube of claim 8 wherein the transition between said emitting and nonemitting areas is a sharp step.
 11. The electron tube of claim 10 wherein said emitting areas are recessed below the surface of said nonemitting areas.
 12. The electron tube of claim 8 wherein said cross section is substantially rectangular.
 13. The electron tube of claim 8 wherein said emitting areas are flush with said nonemitting areas.
 14. The electron tube of claim 8 wherein said nonemitting areas extend radially outward beyond said emitting areas by an amount not exceeding 0.004 inch. 